Process for stabilizing or deactivating sludges, precipitates, and residues occurring or used in the manufacture of tetraalkyl leads



Patented Dec. 9, 1947 UNITE FFECE Adrian L. Linch, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application September 16-, 1942, Serial No. 458,581

6 Claims. 1

This invention relates to a process for stabilizing or deactivating sludges, precipitates and residues occurring or used in the manufacture of tetraalkyl leads, and. which normally tend to pro-mote decomposition and ignition of the tetraalkyl leads that may be contained therein. It is known that alkyl metal compounds in general are quite unstable and decompose readily, particularly in the presence of air or oxygen. It has also been found that these alkyl metal compounds are particularly unstable when adsorbed on materials which present a large surface area per unit volume such as silica gel, clays, alumina, earths, asbestos, charcoal, and materials of similar structure which materials appear to exert a catalytic efiect in the decomposition of these alkyl metal compounds. Even tetraalkyl leads such as tetraethyl lead which is known to be somewhat more stable than some of the other alkyl metal compounds decomposes and often ignites in the presence of oxygen when small amounts are adsorbed on materials that ofier extended surface areas, particularly when the masses containing the tetraethyl lead are exposed to temperatures somewhat higher than normal atmospheric temperatures, The tend ency to oxidize and ignite, of course, varies with the substance with which the alkyl metal compound is incorporated, some materials apparently exerting a greater catalytic effect than others in promoting ignition of the alkyl lead compounds. In the manufacture of tetraalkyl leads, such as tetraethyl lead, tetra-methyl lead and the mixed ethyl-methyl lead compounds, sludges are formed from which it is diflicult and, from a practical standpoint, impossible to entirely free from the alkyl lead compounds during the normal steam distillations or decantation operations. There is, therefore, carried through the process very finely divided lead and impurities such as bismuth compounds which, although present in very small amounts, finally are deposited as sludges in the pipes and tanks and other processing equipment, and these sludges which contain tetraethyl lead adsorbed therein when exposed to oxygen or air often ignite, thus presenting serious ignition and explosion hazards in the process.

Methods have been advanced for the removal of practically all the sludge forming materials from the tetraethyl lead after its distillation, such as by controlled blowing with air or oxygen with agitation, preferably under a layer of water, followed by separation of the precipitated sludge, as more particularly described in copending application Ser. No. 393,680. However, even in these cases the sludges which are deposited by the action of the oxidizing agent and which invariably contain tetraethyl lead, tend to ignite when exposed to air thus presenting serious ignition hazards, making it desirable that. even these sludges should be deactivated during their formation or afterwards to permit of their removal and disposal in a. safe manner.

It is therefore an object of this invention to provide a process for stabilizing sludges, precipitates and residues occurring in the manufacture of tetraalkyl lead compounds whereby the ignition hazard presented by the lead alkyl compounds in contact with such catalytic surfaces is reduced or completely overcome.

It is a still further object of the invention to render inactive materials which tend. to exert a catalytic eliect in the decomposition of tetraalkyl leads in the presence of air thus permitting th safe use of such materials as filter aids in the manufacture of tetraalkyl lead.

I have found that sludges, precipitates and residues occurring or involved in the productionof tetraalkyl leads which offer large surface areas per unit volume and which normally tend to exert catalytic effect and cause decomposition and ignition of the tetraalkyl lead which may be contained therein can be rendered inactive conveniently and conomically by washing or otherwise treating them with solutions or dispersions of quaternary ammonium compounds. These stabilizing or deactivating agents appear to be preferentially absorbed by the active materials, which materials retain their capacity to absorb the tetraalkyl lead, although they no longer have the property of inducing ignition of the tetraalkyl lead absorbed therein.

By the terms sludges, precipitates and residues I include those filter aids which may be employed in the production of the tetraalkyl leads and which offer a large surface area per unit volume and are known to accelerate decomposition of the tetraalkyl leads on exposure to air or oxygen such as clays, silica, earths, charcoal, etc. These filter aids are rendered inactive by treating them with quaternary ammonium compounds either before or after they are employed in the process. The effectiveness of the quaternary ammonium compounds in the deactivation of these active materials is not materially re duced by washing the deactivated materials with Water or other solvents or by drying, them down prior to use.

The quaternary ammonium compounds that may be employed for the purpose of deactivating the sludges, precipitates and residues involved in the manufacture of tetraalkyl leads may vary widely in their chemicalcomposition as will be illustrated by the following examples. The only limitations upon this class of compounds insofar as I have been able to determine is that wher the organic radicals on the nitrogen atom are alkyl groups at least one of such groups should contain at least 8 carbon atoms and that the molecules should not contain a free sulfonic acid group. The sulfonic acid group as such appears to render these compounds incapable of deactivating the sludges. Substituted sulfonic acid groups may, however, be present in the molecules without rendering them inoperative.

As illustrative of the type of quaternary ammonium compounds that may be employed as deactivating agents are those having the general formula .R R Ell/i where:

X=An anion, or togetherwith R1 is oxygen (amine oxide);

R=(1) An alkyl group containing at least 8 carbon atoms; (2) An aralkyl group; (3) An aryl group; or (4) Their substitution products containing a hydroxyl, alkyl, amino, orsubstituted amino group; or (5) R, R2 and N may form a heterocyclic or substituted-heterocyclic ring; or (6) R, R1, R2, and N may form a heterocyclic, or substituted heterocyclic ring system.

R1, R2 and R3=( 1) An alkyl group; (2) An aralkyl group; (3) An aryl group; or -(4) Their substitution products; or (5) Brand Rztogether may be an arylene group.

The quaternary ammonium deactivators are preferably employed as aqueous solutions which contain the deactivating agent in an amount equivalent to-from about one-fourth to threefourths of the dry-weight of the material to be stabilized. The amount of deactivator employed may, of course, be varied over a wide range with equally good results. By employing the stabilizer in an amount ranging from 0;05 %"to more than 100% ofthe dryweight of the active material, satisfactory results have been obtained. The stabilizing effect may-be obtained in some cases by using even smaller amounts of thedeactivating agent, although a sufiicient amount should always be usedto insure complete deactivation of the active material. Theme of excessively a sufficient amount of solution to insure com plete contact of all the material to be deactivated. To prevent the use of unnecessary large amounts of the deactivating agent, it will usually be found desirable to use a relatively large volume of solution of a concentration of less than 5%. Where there is an advantage in employing a lesser volume of solution, the concentration may, of course, be increased.

An important use of the present invention in the commercial manufacture of tetraethyl lead is to deactivate the sludges which are precipitated and removed from the crude tetraethyl lead in the purification step. A method of precipitating and removing these sludges by treating the crude tetraethyl lead with oxidizing agents such as with air or oxygen is more particularly disclosed in copending application Ser. No. 393,680. The precipitated sludges from this process collect in the aqueous layer from which the purified tetraethyl lead is separated by decantation. Although dispersed in the water layer the sludge retains sufficient tetraalkyl lead absorbed therein to ignite on contact with oxygen or air, particularly at slightly elevated temperatures. In order to permit the safe handling and disposition of these sludges, it has been found desirable to deactivate them before they are removed from the system. This can be done conveniently by adding a quantity of one of the deactivating agents to the aqueous sludge dispersion and then agitating the mass to assure complete contact of all the sludge with the deactivating material, or an aqueous 50111-1 tion of the deactivating agent may be used to cover the tetraalkyl lead during the accelerated sludge precipitation treatment so that the sludge is deactivated as fast a it is formed.

The deactivating materialmay be employed in an aqueous solution or suspension or in other solvents.

Where the sludges or precipitates settle out in the pipe lines or other processing equipment during the manufacture or purification of the tetraalkyl leads, they may be deactivated, to insure safety in their removal or during repair of the equipment, by pump ng a solution of one of the'deactivating materials through the apparatus for a suflicient period of time to insure complete contact with all the sludge to be deactivated, which is usually accomplished in'from 15 to 30 minutes. Y

The filter aids may be washed with a solution of the deactivating agent prior to their use in the process. They may be employed either before or after drying, for it'has been found that'they do not again become: active even after being dried,

or by being washed by the solutions that are filtered therethrough.

A further use of the inventionis found in the storage ofcrude tetraalkyl lead before it is desludged by accelerated'sludge precipitation. An aqueous solution of one of the deactivators disclosed maybe used to cover the crude tetraalkyl lead. Any sludge which precipitates-at the surface of the lead alkyl on standing is stabilized by contact with the aqueous layer. If desired, all of the precipitated sludge may be brought into the aqueous layer by suitable agitation since the stabilized sludge particles readily disperse in the water layer. In this way the sludge may be deactivated as soon as it is formed.

The following examples are given to illustrate the invention. The parts used are by weight.

Example 1 Approximately 10,000 parts of crude tetraethyl lead were processed in a washer to precipitate the sludge-forming impurities by the method described in the copending application Ser. No. 393,- 680. The precipitated sludge, which by laboratory analysis of a small sample had been calculated to weigh parts, was collected in 1,000 parts of water. The purified tetra ethyl lead was then decanted from the water layer. Approximately 8 parts of crystal violet (C. I. No. 681) were added to the aqueous phase producing a solution of about 0.8% crystal violet. The mixture was agitated for 15 minutes and filtered.

A small portion of the filter cake was then tested for ignition activity by placing it on a filter paper, wetting the cake with a small quantity of tetra ethyl lead and heating on a steam bath. No signs of ignition or of charring of the filter paper were noted even after 24 hours on the steam bath.

A sample of the same sludge which was taken before the crystal violet was added to the water layer was tested for activity as outlined above. Ignition occurred shortly after the initial sample was placed on the steam bath.

In regular plant application of this method of sludge deactivation, it may not always be convenient to run a laboratory analysis in order to determine the amount of sludge to be expected, and such a procedure is not necessary. I have found that under usual conditions the quantity of sludge formed per 1,000 parts of tetraethyl lead seldom exceeds 2 parts, and this figure may be used as a basis for the calculation of the quantity of deactivator needed. Thus, if I add about 0.5 to 2 parts of deactivating agent to the water layer per 1,000 parts of tetraethyl lead, sufficient deactivator is present to meet any conditions which I have met. Of course, tetraethyl lead manufactured in various plants may vary in sludging capacity depending on quality of raw materials, but in any one plant the quantity is relatively constant, and a definite amount of deactivator per unit weight of tetraethyl lead may be considered as adequate in all cases.

Example 2 Approximately 1,000 parts of crude tetraethyl lead were placed in a suitable container provided with means for agitating its contents. About 200 parts of water were added and the sludge was precipitated and collected in the water layer as disclosed in the previously mentioned application Ser. No. 393,680.

After the precipitation treatment was complete, two parts of octadecyl trimethyl ammonium bromide were added, and the contents of the container were agitated for about 15 minutes. The tetraethyl lead and the aqueous layer were then filtered together, and the clear tetraethyl lead were decanted from the water layer after filtration was complete. A sample of the sludge retained on the filter was tested for ignition activity as previously described and was found to be inactive. Sludge obtained using the same crude tetraethyl lead and the same process,

except that no octadecyl trimethyl ammonium bromide was added, produced ignition of the tetraethyl lead when placed on the steam bath.

It is, of course, understood that other quaternary ammonium compounds may be employed in these examples in place of the crystal violet or the octadecyl trimethyl ammonium bromide. The quantities and concentrations employed in these examples are given to illustrate the invention and not as limitations thereupon, and they may be varied widely without altering the results obtained.

While in the preceding examples I have illustrated the use of stabilizing agents which dissolve in neutral aqueous solutions, it is to be understood that deactivating agents which are insoluble in aqueous solutions may be effectively applied from suitable basic or acid solutions or from solutions in organic solvents. Where water or anaqueous solution is used as the solvent or dispersing medium, the method of applying the deactivator to precipitated tetraalkyl lead sludges is effective when applied as set forth in Examples 1 and 2. However, when the use of some solvent other than water is convenient, the aqueous layer containing the sludge may be filtered first, and the filter cake then agitated with the solution containing the stabilizing agent for 15 to 30 minutes, or the solvent solution may be added directly to the aqueous sludge suspension.

It has been found that where 10 parts of an active sludge are agitated with 50 parts of a 1.0 to 2.0% solution of the following representative quaternary ammonium compounds, the sludges are completely deactivated so that they show no tendency to ignite when heated at steam bath temperatures for periods as long as 72 hours: Methylene blue (C. I. No. 922), neutral red (C. I. No. 825), acridine orange (C. I. No. 788), steara'midomethyl pyridinium chloride, brilliant cresyl blue (C. I. No. 8'77), lecithin, rhodamine B (C. I. No, 749), crystal violet (C. I. No. 681), phenosafranine (C. I. No. 840), dimethyl stearyl amine oxide, fuchsine (C. I. No. 677), octadecyl trimethyl ammonium bromide, benzyl dioctyl methyl ammonium chloride, para amino benzyl trimethyl ammonium chloride, par octyl phenyl trimethyl ammonium iodide, hexamethylene tetramine addition compound with para hydroxy chloracetyl benzyl amine, 1-4 di(N-chloro pyridyl acetyl amino) anthraquinone, a-(N-chloro betainyl) amino azo benzene, and phenyl benzyl dimethyl ammonium chloride. Where the untreated sludge employed in these tests was subjected to the same ignition test, it ignited shortly after being placed on the steam bath.

As previously stated the invention may be employed to stabilize active filter aids which are to be used in tetraalkyl lead filtration. These materials may be washed in a solution of one of the deactivators and rendered suitable for tetraalkyl lead filtration. The following filter aids as well as a number of other materials of similar structure were wet with tetraethyl lead and placed on a steam bath as described in Example 1 above. All were found to initiate the ignition of tetraethyl lead. Ten parts of each of these materials were then agitated for several hours with 50 parts of the solution of various quaternary ammonium compounds of the concentrations iven in the following table. Where no solvent is specified, water is used. After the agitation period, the solutions were filtered and portions of the filter cakes were wet with tetraethyl lead and p acedpn a steam bath. Results of-the, tests are, given below: 1 Filteraid (clay)... l :Ignited. D'o'.. No decompo- N0. 681 3 sltion. Filter aid (silica) None... Ign ted.-

Do 1% Methylene Blue (011. Nodecompo- N o. 922). sition. Yeillowl Lead Oxide (N. None a Ignited. i

b0. .No decomposition;

Ignited.

Bismuth Subnit-rate None Do 2% octadecyl trimethyl Nodecompoammonium chloride. sition. Bismuth Oxide (from None Ignited.

hydrolysis of Bi- (N Oak). I Do 2% Acridine Orange (0. I. N odecompo- N o. 788). sition. Ferric Oxide (anh.) None Ignited.

Do 1.5% Dimethyl stearyl- No d ecompoamine oxide in 50% sition. ethanol.

Activated alumina None Ignited.

Do l% Stcaramidomethyl No decompopyridinium chloride. sition. Decolorizing charcoal.. one Ignited.

Do 2% Brilliant Cresyl Blue Nodecompo- (O. I. No. 877). sition.

Example 3 Approximately 20,000 parts of crude tetraethyl lead were placed in a suitable tank or washer, and approximately 5,000 parts of water were added to the tetraethyl lead. Some 40 parts of lecithin were then added to the water layer, and the sludge was precipitated and removed from the tetraethyl lead by the method disclosed in the copending application Ser. No. 393,680. After this operation was complete, the tetraethyl lead was removed by decantation, and the aqueous layer containing the sludge was filtered. A portion of the filter cake was then tested on the steam bath as described in Example 1. No decomposition or ignition of the tetraethyl lead was noted.

Example 4 As previously stated, sludges found in tetraethyl lead are also found in other lead alkyls which are manufactured from commercial lead. An example of these alkyls is the mixed tetramethyl-ethyl compounds of lead, formed when a mixture of methyl chloride and ethyl chloride are reacted with lead sodium alloy. All examples in which tetraethyl lead is specified are equally workable with these mixed lead alkyls.

Approximately 1,000 parts of crude mixed tetramethyl-ethyl lead compounds (tetramethyl lead, trimethyl ethyl lead, dimethyl diethyl lead, methyl triethyl lead and tetraethyl lead) were placed in a suitable tank or washer, and 100 parts of water containing 1 part of neutral red (C.'I. No. 825) were added. The contents of the tank were aerated and agitated for two hours as disclosed in the copending application Ser. No.

393,680. After a settling period of a few minutes,

the clear mixed lead alkyls were decanted from the aqueous layer, and the aqueous mixture was filtered. A portion of the filter cake was tested on the steam bath as described in Example 1, ex-

7 cept that the filter cake (sludge) waswet with mixed lead alkyl compounds rather ,-than with tetraethyl lead. No decomposition or ignition of was carried out in which no stabilizing agent was placed in the water layer. This sludge ignited the mixed alkyls when the steam bath stability test was made.

the lead alkyls was noted. A similar experiment .to ignite under the conditions employed,,if the sludge was not fully inactivated, for in some instances, it is possible that the amount of alkyl lead may be reduced to such a small amount that ignition frnight'not be noted. While the elimination bfflthe alkyl lead from the residues to such anextent does'not'ordinarily'takeplace, the tests were made under conditions favoring ignition provided the sludge or filter aid was active.

This invention makes'possible the deactivation of the ignitable sludges and residues occurring in the manufacture of tetraalkyl lead compounds and is of particular value in eliminating fire and explosion hazards involved in the removal and disposal of such sludges from the process and in overcoming the potential fire hazard arising from the collection of such sludges and precipitates which accumulate in various places in the processing equipment and which when exposed to air often ignite with considerable damage. The invention also permits the use of filter aids which,

unless rendered inactive, tend to cause ignition of any absorbed tetraethyl lead when theyare exposed to the air. Any other absorbent materials which for any reason may become saturated with tetraethyl lead in or about the plant in which it is being manufactured may be rendered inactive by washing or otherwise treating with stabilizersexposed to oxygen, which comprises washing such sludges with a quaternary ammonium compound in an aqueous medium.

2. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises washing such sludges with a quaternary ammonium compound in an aqueous medium.

3. The process for inhibiting the spontaneous ignition of tetraalkyl lead compounds adsorbed on sludges which are precipitated from crude tetraalkyl lead compounds and which sludges normally tend to cause spontaneous ignition of the tetraalkyl lead compounds adsorbed thereon when exposed to oxygen, which comprises washing such sludge-s with a quaternary ammonium compound in an aqueous medium in an amount sufficient to provide at least 0.05% of the quaternar-y ammonium compound on the dry weight 70.

of the sludges. V V

a. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed and which sludges normally tend to cause spon- 15 2,165,651

10 taneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which ccmprises washing such sludges with lecithin in an aqueous medium.

ADRIAN L. LINCH.

REFERENCES CITED The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS Number Name Date 2,155,678 Osterhout Apr. 25, 1939 Rees et a1 July 11, 1939 Certificate of Correction Patent No. 2,432,321. December 9, 1947. ADRIAN L. LINCH It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 10, list of references cited, under the heading UNITED STATES PATENTS add the following- 1,863,451 Profiitt "June 14, 1932 and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 10th day of February, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommz'esiomr of Patents.

Certificate of Correction Patent No. 2,432,321. December 9, 1947. ADRIAN L. LINCH It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 10, list of references cited, under the heading NITED STATES PATENTS add the following- 1,868,451 Proflitt June 14, 1932 and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 10th day of February, A. 1948.

THOMAS F. MURPHY,

Assistant Uommissioner of Patents. 

